1. Field of the Invention
The present invention relates to a technique for tracking an object in a specific area in a moving image.
2. Description of the Related Art
Conventionally, in an image processing apparatus such as a digital camera or digital video camera, a technique for detecting, by means of an image process, an object set by a photographer or an object pattern which is set in advance in a captured moving image, and tracking that object is known. In such an object tracking techniques based on the image process, a position having a high correlation with the object pattern in an image is determined as a moved position of the object. For this reason, when an imaging range includes an analogous pattern, or when a new analogous pattern enters the imaging range, the object may fail to be recognized.
Japanese Patent Laid-Open No. 11-150676 discloses a technique which detects a moved position of an object by calculating a degree of correlation in a search area using a color-difference histogram of an object to be tracked as a template, and directs a camera in the direction of the object, thereby improving the tracking performance.
However, when the degree of correlation is determined using a set histogram pattern (feature amount) of the object as in Japanese Patent Laid-Open No. 11-150676, the feature amount often changes due to a change in imaging condition, and a wrong object may be tracked or it becomes impossible to track any object. For example, when the set feature amount of the object includes a hue range, if the object has low saturation, and if the brightness of the object changes depending on an illumination condition, the feature amount distribution also changes, and extraction of a high-correlation area often fails.
When the imaging range includes a color analogous to that of the object, the analogous color may be erroneously discriminated as the object, and a wrong object may be tracked.